How can I convert uppercase letters to lowercase in Notepad++

First select the text
To convert lowercase to uppercase, press Ctrl+Shift+U
To convert uppercase to lowercase, press Ctrl+U

Just select the text you want to change, right click and select UPPERCASE or lowercase depending on what you want.

Ctrl+A , Ctrl+Shift+U

should do the trick!

Edit: Ctrl+U is the shortcut to be used to convert capital letters to lowercase (reverse scenario)

In my notepad++ I press

Ctrl+A = To select all words

Ctrl+U = To convert lowercase

Ctrl+Shift+U = To convert uppercase

Hope to help you!